1. Technical Field
The present invention relates generally to a method of producing rolling codes and a keyless entry apparatus using the same, and more particularly to a rolling code producing method of producing a sequence of different codes for ensuring high entry security and a keyless entry apparatus using the same.
2. Background of Related Art
Keyless entry systems are well known in the art for securing anti-theft characteristics in automotive vehicles. In a typical keyless entry system, a transmitter installed in a key transmits an identification code to a receiver mounted in the vehicle to determine whether the transmitted identification code is correct or not. If it is correct, doors and an alarm system are released. This offers a higher degree of security than that of mechanical key entry systems.
Since such keyless entry systems usually use a single identification code, the entry security is, as described above, improved greatly but it is not enough to ensure complete entry security.
In order to alleviate such problems, the following steps are provided:
(1) A rolling code wherein an identification code is changed every communication between a transmitter and a receiver; PA0 (2) The rolling code is further scrambled or encrypted as a random code; and PA0 (3) The algorithm for producing the rolling code is changed every communication of the code between the transmitter and the receiver.
These steps however still do not produce totally satisfactory results. For example, simple usage of the rolling code as in (1) may allow a subsequent rolling code to be estimated based on a known code. When the number of figures of the random code as in (2) is small, it can be easily decoded by using all possible combinations of numbers of the same figures as those of the random code. Additionally, if the same operation is performed whenever the rolling code is scrambled, the algorithm for producing the rolling code may be easily decoded based on a change in output of the code.
Changing the algorithm as in (3) requires a storage memory having a large enough capacity to store different programs, one for each algorithm. Particularly, a portable transmitter of the keyless entry system needs to be compact and to exhibit rapid response, and therefore the capacity of the storage memory and the algorithms for scrambling the rolling code need to be small and simple, respectively.
The above problems are also encountered in keyless entry systems for use in houses or office buildings and keyless access systems for use in lockers of the type which uses encrypted access codes to for avoid unauthorized access.